The Carrier Sense Multiple Access/Request to Send—Clear to Send (CSMA/RTS-CTS) protocol used in 802.11 will now be summarized. Drawing 100 of FIG. 1 shows a typical time line of events under the CSMA/RTS-CTS protocol when two links compete for medium access. In this example node A 102 and node C 106 are the two transmitters with intended receivers being node B 104 and node D 108, respectively. Various elements in this 802.11 protocol are described in the example below.                1. Each of the nodes (102, 104, 106, 108) waits for a determined time interval, Distributed Coordinated Function (DSC) Interframe Spacing (DIFS) 110 to sense ongoing transmissions.        2. After DIFS 110 is completed, each of the nodes (102, 104, 106, 108) picks a random collision window (CW). A node is not allowed to send out an RTS signal during its CW window. During CW, the node keeps carrier sensing and a node is allowed to send out an RTS subsequent to its CW window if the energy level sensed during its CW is below a predetermined threshold. In this example, consider that both node A 102 and node C 106 would like to send out RTS signals; however, consider that node A's CW is shorter than node C's CW. Therefore when the node A CW 112 ends, node A 102 generates and sends out a RTS 114. At this time node C 106 is still sensing in its CW and detects energy above a predetermined sense level, and is precluded from transmitting an RTS.        3. After receiving RTS 114, the intended receiver, node B 104, generates and sends out the CTS signal 116.        4. After node A 102 receives CTS 116, node A 102 generates and transmits the data transmission signal 118, which is received and recovered by node B 104. Node B 104 generates and transmits the ACK signal 120 which is received and recovered by node A 102.        5. Both RTS signal 114 and CTS signal 116 include information indicating the length of time intervals for the transmission to complete. Each of the devices which overheard the RTS or CTS messages and are not part of the communications link (node C 106 and node D 108) remain silent during the time interval communicated in the RTS signal 114 and CTS 116 signal, denoted as NAV period 122. This protocol is usually referred to as the virtual carrier sensing.        6. Now, at the next determined time interval, DIFS 124, each of the nodes (102, 104, 106, 108) senses ongoing transmissions.        7. After DIFS is completed, each of the nodes (102, 104, 106, 108) picks a random collision window (CW). In this example, consider that either (i) both node A 102 and node C 106 would like to send out RTS signals; however, consider that node C's CW is now shorter than node A's CW or (ii) node C 106 would like to send out an RTS signal, but node A does not desire to send out an RTS signal at this time. Therefore when the node C's CW 124 ends, node C 106 generates and sends out a RTS 126. At this time node A 102 is still sensing in its CW and detects energy above a predetermined sense level, and is precluded from transmitting an RTS if it wants to.        8. After receiving RTS 126, the intended receiver, node D 108, generates and sends out the CTS signal 128.        9. After node C 106 receives CTS 128, node C 106 generates and transmits the data transmission signal 130, which is received and recovered by node D 108. Node D 108 generates and transmits the ACK signal 132 which is received and recovered by node C 106.        10. Both RTS signal 126 and CTS signal 128 includes information indicating the length of time intervals for the transmission to complete. Each of the devices which overheard the RTS or CTS messages and are not part of the communications link (node A 102 and node B 104) remain silent during the time interval communicated in the RTS signal 126 and CTS 128 signal, denoted as NAV period 134.        
Note in the current 802.11 protocol, each of the 802.11 protocol signals (114, 116, 118, 120, 126, 128, 130, 132) are transmitted at a predetermined, e.g., maximum, transmit power level. Also note that short InterFrame Spaces (SIFS) occur between the RTS and CTS, CTS and DATA, and DATA and ACK signals.
Current 802.11 PHY/MAC is not tailored for optimizing spatial reuse in large scale ad hoc network deployments. In particular, the carrier sensing protocol prevents two links from transmitting simultaneously whenever the two transmitters are within each other's carrier sensing range. This leads to overly conservative spatial reuse since if the two links are short links, they may be able to transmit simultaneously without causing too much damage to each other, if they were allowed to do so. Current carrier sensing based protocols, including RTS/CTS based yielding protocols, are based on a static energy threshold.
In view of the above discussion, it should be appreciated that there is a need for improved methods which would increase the chances for multiple devices to transmit at the same time when such transmissions do not prevent the device to which a signal is transmitted from recovering the transmitted signal.